High moisture resistance of an efficient Mn4+-activated red phosphor Cs2NbOF5:Mn4+ for WLEDs

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 405; p. 126678
• Main Authors: Zhou, Jianbang, Chen, Yingyuan, Jiang, Chunyan, Milićević, Bojana, Molokeev, Maxim S., Brik, Mikhail G., Bobrikov, Ivan A., Yan, Jing, Li, Junhao, Wu, Mingmei
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-02-2021
• Subjects: Light-emitting diodes; Mn4; Moisture resistance; Photoluminescence; Self-protection; Moisture resistance; Mn4; Self-protection; Light-emitting diodes; Photoluminescence
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2020.126678

Nb5+ is proved to play a major role in improving the moisture-resistant performance of Mn4+ by self-suppressing the hydrolysis of [MnF6]2− groups, which may provide a new approach to substantially improve the waterproof stability of Mn4+-activated (oxy)fluoride red phosphors.
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•Cs2NbOF5:Mn4+ shows much better moisture resistance than fluoride red phosphor.•Nb5+ is proved to play a leading role in improving the water-resistant properties.•The water resistance of Mn4+-activated fluorides can be improved by Nb5+.•Warm WLEDs with high luminous efficacy of 174 lm/W have been fabricated.
Mn4+-activated fluoride red phosphors, the most important red phosphors for warm white light emitting diodes (LEDs), usually suffer from inherent poor moisture resistance which is a major obstacle to their long-lasting outdoor applications in a high humidity environment. Surface modification of phosphors by coating with either organic or inorganic shells is an effective way to improve waterproof stability. However, the coating procedure usually has a negative impact on the luminous efficacy due to the increased passivation shell thickness. In this work, Mn4+-activated oxyfluoroniobate (Cs2NbOF5), a highly efficient phosphor with internal quantum efficiency of ca. 82%, has been successfully synthesized and it is interesting to note that Cs2NbOF5:Mn4+ can exhibit remarkably improved waterproof stability even without surface coating compared to well-accepted commercial fluoride red-emitting phosphor, K2SiF6:Mn4+. The results obtained indicate that Nb5+ ions inside red phosphor play a crucial role in improving the water-resistant performance of Mn4+, which provides a new concept for overcoming the downside of their waterproof in humid conditions and maintaining the luminescence efficiency. In the final phase white LEDs with a high luminous efficacy of 174 lm/W (higher than commercial fluoride red phosphors), low correlated color temperature (3164 K) and high color rendering index (Ra = 90 and R9 = 85) have been fabricated using Cs2NbOF5:Mn4+.